1. Field of the Invention
The present invention relates to an air cavity module for a planar type filter operating in millimeter-wave frequency bands and, more specifically, to an air cavity module for a planar type filter operating in millimeter-wave frequency bands, in which cavity resonance is eliminated from an air cavity for a planar type filter and the planar type filter is completely mounted in the air cavity, so that both transmission loss and radiation loss can be reduced to improve the characteristics of the filter that operates in the millimeter-wave frequency bands.
2. Discussion of Related Art
In general, as the development of wireless communication technology has been accelerated and the amount of processed data has increased, the operating frequency of wireless, communication systems has been spontaneously reaching millimeter-wave frequency bands on the order of several tens of GHz or higher. In this connection, components for the wireless communication systems have been scaled down in size, and above all, a radio frequency (RF) filter, which is a passive component, has been scaled down to such a small size that it can be made using a semiconductor process.
Also, as the operating frequency of the wireless communication systems becomes higher and the RF filter becomes smaller, the RF filter is more susceptible to the environment and may be seriously damaged due to radiation loss.
It is difficult to find an exemplary conventional technique of an air cavity for a planar type filter that operates in the frequency band on the order of several tens of GHz or higher because the technique is not yet generalized. However, there is a disclosure having similar objects, which is directed to a ceramic package for a surface acoustic wave (SAW) filter that operates in low frequency bands. In the disclosure, a filter is mounted in the ceramic package, and an electrode of the filter and an electrode of a ceramic module are connected using a wire bonding process, thereby enabling the transmission of signals.
The above-described ceramic package is aimed at protecting components against external shock and, particularly, protecting the SAW filter, which is susceptible to the environment, by cutting off externally generated electromagnetic waves.
However, once the operating frequency of the SAW filter exceeds several tens of GHz, the SAW filter may be damaged, the bonded wire itself may operate as a parasitic factor, and transmission loss may increase.
As another similar example, there is a receiver for a wireless communication system that operates in the frequency band of 20 GHz. The receiver for the wireless communication system is formed as a system on packaging (SOP) type on a multilayered benzocyclobutene (BCB) layer formed on a silicon substrate.
In this case, components as active devices are bonded as a flip-chip onto the BCB layer. A dual mode resonator (DMR) pattern is printed as an inverted microstrip line (IMSL) on the BCB layer, and a planar type fitter as a passive device is covered by and bonded to a cavity, which is obtained by etching the surface of the silicon substrate to a shallow depth using a dry etching process and covering the etched surface with a metal.
Because all the components are mounted on the line printed on the same substrate, interconnection loss between the components may be reduced. Also, the cavity formed in the silicon substrate covers the planar type filter so that transmission loss may be lessened.
However, since the planar type filter is not completely mounted in the cavity, signals are leaked through the silicon substrate on which the BCB layer is formed, thus resulting in great transmission loss and poor attenuation characteristics.